This invention is directed to corrosion inhibitors for metallic surfaces which come into contact with aqueous preparations and for a method of inhibiting corrosion of such metal surfaces. More particularly, this invention concerns methylpolysiloxanes which are effective corrosion inhibitors for such metallic surfaces.
Metallic surfaces which come into contact with aqueous preparations such as heat-transfer media, coolants, drilling and cutting oil emulsions, in the presence of oxygen, are easily corroded. To avoid such corrosion, numerous inhibitors known in the art are used, most of which contain nitrogen or phosphorus atoms.
For example, metal processing emulsions for metal shaping (cutting, shaping by deep drawing and rolling) are claimed in German Patent 2,907,863. These emulsions are of the oil-in-water type, have good stability, can be infinitely diluted and are based on triglyceride oils. As dermatologically safe wetting agents with a corrosion inhibiting effect, the emulsions contain alkanolamines with 2 to 4 carbon atoms in the alkanol portion or fatty acid salts thereof. In the same way, fatty amines which contain 8 to 18 carbon atoms are also supposed to prevent rust.
In German Patent 3,015,864, polyoxyalkylenediamides with terminal carboxylic acid groups and their salts are recommended as corrosion-inhibiting additives for metal processing emulsions. These products reportedly improve the lubricating properties of the preparation at the same time.
Compounds of the following structure are claimed in U.S. Pat. No. 3,389,160: ##STR1## In this formula R is a univalent hydrocarbon group with up to 18 carbon atoms,
R' is a divalent hydrocarbon group with up to 18 carbon atoms or a divalent hydrocarbon oxy group with up to 18 carbon atoms, the oxygen in the hydrocarbon oxy group being present in the form of an ether bond and the hydrocarbon portion of the hydrocarbon oxy group being present in the form of a divalent alkylene group, PA1 X is the anion of an acid, PA1 R" is hydrogen or, when X is a halogen atom, either hydrogen or a group such as R PA1 a=0 or 1, PA1 x has an average value of 1 to about 100, PA1 y has an average value of 0 to about 1,000 and PA1 the ratio of y:x is not greater than 50:1. PA1 R.sup.3 and R.sup.4 are the same or different in the molecule and represent an alkyl group with 1 to 4 carbon atoms, PA1 Z is the ##STR6## group, X.sup.(-) is an inorganic or organic anion, PA1 n has a value of 5 to 20, PA1 m has a value of 1 to 10, and PA1 the ratio of the number of dimethylsiloxy groups to the number of quaternary ammonium groups has a value of 0.5 to 15. PA1 p has a value of 1 to 29.
Various applications have been indicated for compounds of general formula I.
Compounds of general formula ##STR2## are useful as corrosion inhibitors for aqueous systems. It is a disadvantage, however, that these compounds have only very slight solubility in water, and as a result, these compounds must be emulsified or a solubilizer must be used in an aqueous system.
Compounds of the formulas ##STR3## are reported to reduce the surface tension of water and to be surface active substances. It cannot be inferred from U.S. Pat. No. 3,389,160 that the compounds of formulas III and IV are usable for the purpose of inhibiting corrosion.